I am not 100% sure of authenticity ChatGP believes it to be real based on a variety of factors such as item code, the Campeones wording on the rear, the rough era. 

The original owner said they got it in Buenos Aires and everything I have checked appears to check out. I can only see one other example of this shirt on the internet, and the appears to be from a credible supplier also.

Has had a repair on the left armpit it looks like, rear numbering is peeling slightly